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  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
  </head>
  <body>
    <script>
    // let sum
    // let arr = [11, 22, 33]
    // for (let i = 0; i <= arr.length; i++) {
    //   sum += arr[i]
    // }
    // console.log(sum)

    let sum = 0
    let arr = [11, 22, 33]
    for (let i = 0; i < arr.length; i++) {
      sum += arr[i]
    }
    console.log(sum)
  </script>
  </body>
</html>